The invention is related to a method and a device for manufacturing a three-dimensional object by a successive linear solidification of layers of a building material at positions in the respective layer corresponding to the cross-section of the object.
In laser sintering as well as in stereolithography and other related layer-wise manufacturing methods there are known various exposure patterns for filling regions, i.e. regions that are located in the respective layer inside of the contour defining the outline of the object.
In particular in order to minimize shrinkage effects and residual stress there have been developed exposure patterns that divide the area to be exposed into partial areas and expose these in differing sequences if necessary. Such exposure patterns are for example described in EP 0 429 196 B1, DE 42 33 812 C1 for stereolithography and in DE 100 42 134 C2 for laser sintering. Typically, the direction of the exposure vectors is rotated by 90° from layer n to layer n+1, leading to the same exposure orientation in each second layer. Also in electron beam sintering special exposure methods such as a helical or a meandering exposure of partial regions are used as described in WO 2004/056509.
From EP 0 590 956 A1 an exposure method for stereolithography is known, in which a light beam is directed across a layer in a plurality of vectors that are in parallel, wherein the direction of the vectors changes from one layer to the successive layer by 180°, 90° or 45°. These methods have disadvantages. In each layer material properties are created having a preferred orientation or for an exposure with crossing directions two preferred orientations. An anisotropy that results from a numerous repetition of few exposure directions leads to a spoiling of the mechanical properties of the whole part. Also the quality of the surface may be affected, e.g. pore formation may occur.
Moreover, there are known further exposure methods for laser sintering—mainly in order to avoid warpage—such as a spiral exposure as in U.S. Pat. No. 6,676,892 B2 or an onion-ring-like exposure as described in DE 101 12 591 A1. These methods vary the exposure directions within a layer, however, typically repeat the same exposure direction at many positions in layers that lie one on top of the other. Therefore, these methods have similar disadvantages.